Grass-fed beef is low in fat, meaning that it requires less cook time and your biggest enemy is overcooking. This is normally fine for beef that is rare to medium rare. But, if you prefer to have your beef cooked well-done, you'll need to cook in low temperatures in a sauce to keep the beef tender and moist.
We recommend using a meat tenderizer or marinade to help break down the connective tissue. If you prefer to not to use a marinate, or don't have a tenderizer, cover your meat with plastic and pound it a few times. A rolling pin or other safe item will suffice. Don't flatten the cut unless the recipe you are using calls for it.
Always bring your meat up up to room temperature before cooking.